Polychlorotrifluoroethylene (PCTFE) is a semi-crystalline polymer with high transparency to visible light and excellent moisture barrier and oxygen barrier properties. PCTFE also has good chemical and thermal stability. However, PCTFE is not soluble in commonly used organic solvents, which prevents PCTFE from use in many applications, such as coatings and membranes. Polyvinyl chloride (PVC) is a low cost plastic polymer with good chemical stability, but it is brittle. Plasticizers are needed to improve PVC's flexibility and processability.
Chlorotrifluoroethylene (CTFE) has been copolymerized with different co-monomers, such as ethylene and vinylidene fluoride, to obtain the corresponding copolymers with the desired properties. Chlorotrifluoroethylene (CTFE) and vinyl chloride (VC) copolymer is one of these CTFE-based copolymers. Applicants have come to appreciate, however, that the prior CTFE/VC copolymers have certain disadvantages.
In U.S. Pat. No. 2,915,506, chlorotrifluoroethylene (CTFE)/vinylidene fluoride (VDF)/vinyl chloride (VC) terpolymers were disclosed. The presence of vinyl chloride in the terpolymers facilitated the ease of cross-linking or vulcanization to a degree not otherwise obtainable if only the copolymer of trifluorochloroethylene and vinylidene fluoride were to be processed. However, the synthesis and composition of chlorotrifluoroethylene/vinyl chloride copolymers is not addressed.
U.S. Pat. No. 4,515,927 discloses a process for suspension polymerization of vinyl chloride and chlorotrifluoroethylene. The object of the process disclosed in the '927 patent is to make a copolymer having a relatively constant weight ration of from about 75 to 95 weight percent vinyl chloride and from 5 to 25 weight percent chlorotrifluoroethylene that is independent of the conversion. The '927 patent discloses that vinyl chloride is known to be more reactive than chlorotrifluoroethylene and as a result the vinyl chloride tends to react more rapidly and the monomer mixture rapidly becomes vinyl chloride-poor. Prior processes, including the process of the '927 patent, therefore used the technique of adding vinyl chloride in a step-wise manner to reconstitute the initial ratio of the vinyl chloride to chlorotrifluoroethylene charge prior to reaching the conversion where the weight ratio of the vinyl chloride and chlorotrifluoroethylene in the copolymer changes. In the process of the '927 patent, the process begins with an initial charge of vinyl chloride in the reactor and then after the polymerization reaction is initiated, additional vinyl chloride was added in a total of from 2 to 5 stages in sufficient quantity to copolymerize from 1 to 20 percent by weight of the unreacted monomers prior to the next addition of vinyl chloride (see Examples 2-7). The process of Example 5 of the '927 patent, for example, utilizes a five-stage VC addition process and achieves an 81.2% overall yield of copolymer and produces a copolymer having a VC/CTFE weight ratio of 80/20, a molecular weight of 66,300, and a glass transition temperature (Tg) of about 33° C.
U.S. Pat. No. 4,702,961 discloses a method of melt processing stabilized vinyl chloride/chlorotrifluoroethylene copolymer with an organo-metal stabilizer using the process as disclosed in the '927 patent.
Applicants have found that the prior processes for producing VC/CTFE copolymers produce polymeric materials with certain disadvantages. For example, the copolymers produced in accordance with the teachings of the '927 patent have molecular weights below about 70,000 and glass transition temperatures that of about 33° C.-34° C. Applicants have found that it is possible to produce novel copolymers of VC and CTFE that have much higher molecular weights and glass transition temperatures than the copolymers produced by the prior process of the '927 patent. Furthermore, applicants have found that the higher molecular weight and higher Tg copolymers produced by the present invention have significant and important advantages in many applications compared to the copolymers of VC and CTFE produced by the prior processes.